The present invention relates generally to motor mounting arrangements and to methods of making the same that are particularly useful in connection with mounting a motor to a bulkhead, baffle, or other suitable motor supporting structure of a product in which such motor is used. Examples of such products are: room air conditioners, air circulation fans, blowers utilized for various air moving or air exhaust applications, and so forth.
In direct drive applications, i.e., applications where blowers or fans are mounted directly to a motor shaft, it is important to isolate motor vibrations from the bulkhead or other mounting surface. It is, of course, desirable to minimize the transmission of all modes of vibrations; but for the reasons pointed out in detail in the above-referenced Litch application, it is especially desirable to minimize the transmission of noise associated with torsional mode motor vibrations. In particular, the noise associated with torsional mode vibrations of twice line frequency and harmonics thereof tend to be very objectionable.
The approaches suggested by Litch constitute advances in the art, although there may be some difficulty in applying those approaches for some applications or under some circumstances. For example, there may be difficulty if the motor itself is manufactured by a process such that motor parts are secured together by structural adhesive materials; or if the motor is of relatively small mass and output, with the result that special manufacturing methods must be adhered to. More particularly, if a motor stator and bearing system is to be assembled and held together by structural adhesive material such as epoxy (as taught, for example, in Thompson et el U.S. Pat. No. 3,165,816, or Rutledge U.S. Pat. No. 3,195,222), it may not desirable from a manufacturing standpoint to have mounting arms or lugs attached to the shell of the motor during the assembly process. Moreover, for motors of relatively small mass and diameter (and thus relatively small polar moments of inertia of the motor mass), where suitable torsional mode vibration isolation is to be accomplished by suitably reducing the transmissibility of the mounting arms or lugs of torsional mode vibrations, difficulties may be encountered because the dimensions of the motor mounting arms or lugs may have to be reduced to such a size that manufacture thereof may be difficult, specially if the radial length of the arms is to be relatively small.
When martensitic steel is utilized to support a relatively small motor (for example, a motor weighing about 2.7 kilograms and approximately three and eight-tenths inches in diameter), and the mounting bolt-hole circle is approximately seven inches in diameter; martensitic steel mounting arms should be only about 0.0010 of an inch thick for good torsional vibration isolation. However, material this thin generally would be difficult to handle in high volume manufacturing operations and often would not possess sufficient strength to withstand at least some shock loading conditions.
It will therefore be understood that it would be desirable to provide new and improved mounting arrangements for motors wherein such mounting arrangements are characterized by improved torsional vibration isolation characteristics, and yet which may be easily manufactured and assembled with motors that are secured together with structural adhesive materials.
Still other problems are encountered for particular application where a torsionally flexible mounting arrangement is desired. For example, mounting a motor within a Sirroco blower housing presents a problem because the sidewall of such a blower is shaped in a logrithmic spiral to provide for the gradual expansion of the air flow expelling from one or more squirrel cage blower wheels attached to the motor shaft (or shafts). However, since the blower wheel (or wheels) is positioned relative to the housing to provide running clearances as desired, the motor often will not be positioned such that it is equadistantly located from two or more points along the periphery of the housing. This type of situation is particularly troublesome when blower wheels are placed at each side of a double shaft motor in order to achieve a full inlet at either side of the blower housing, and the motor is to be mounted internally to the sidewall of the housing rather than to an end wall as in a double inlet blower wheel application where air is taken in at both ends of a single wheel.
In some applications such as, for example, range or oven exhaust fan applications; severe shipping shock tests may not require a motor mounting arrangement that is as stiff in the axial and radial modes as a larger appliance such as a furnace. In fact, many small fan applications make use of elastomeric devices so that effective suppression of radial and axial mode vibrations will result. In some applications, however, a rubber mount may present a safely hazard.
For example, in range or oven applications, a rubber mount may serve as an accelerator in the advent of a grease fire. Moreover, the use of a rubber mount may interfere with establishing a reliable ground connection. It therefore will be understood that it would also be desirable to provide a new and improved motor mounting arrangement that was resilient in radial as well as axial and torsional modes and yet was neither a potential grease fire accelerator nor a potential ground connection failure.
Accordingly, it is a general object of the present invention to provide new and improved motor mounting arrangements and methods of making the same whereby the above-mentioned and other problems may be solved.
It is a more particular object of the present invention to provide a new and improved motor mounting arrangement and methods of making the same, that includes mounting arms which are made of material having sufficient thickness that the manufacture of such arms is facilitated and yet wherein the vibration transmissibility of such arms in objectionable frequency ranges is not objectionably increased because of the material thickness, and wherein the arrangement is mountable in a blower housing having a spiral surface.
It is a further object of the present invention to provide new and improved motors and lug assemblies, as well as methods and means of interconnecting the same, wherein two or more lugs or arms of different lengths are used to mount a motor relative to a blower housing and wherein the arms are tuned so as to have mutually equivalent flexibility and torsional resiliency.
Still another object is to provide a mounting arrangment wherein a satisfactory mounting system may be provided that has very few component parts.
Yet another object of the present invention is to provide a mounting arrangement that is effective for reducing vibrations in modes other than the torsional mode and that also avoids grease fire accelerator and ground connection problems.